A Sparse SCF algorithm and its parallel implementation: Application to DFTB

We present an algorithm and its parallel implementation for solving a self consistent problem as encountered in Hartree Fock or Density Functional Theory. The algorithm takes advantage of the sparsity of matrices through the use of local molecular orbitals. The implementation allows to exploit efficiently modern symmetric multiprocessing (SMP) computer architectures. As a first application, the algorithm is used within the density functional based tight binding method, for which most of the computational time is spent in the linear algebra routines (diagonalization of the Fock/Kohn-Sham matrix). We show that with this algorithm (i) single point calculations on very large systems (millions of atoms) can be performed on large SMP machines (ii) calculations involving intermediate size systems (1~000--100~000 atoms) are also strongly accelerated and can run efficiently on standard servers (iii) the error on the total energy due to the use of a cut-off in the molecular orbital coefficients can be controlled such that it remains smaller than the SCF convergence criterion.Comment: 13 pages, 11 figure

Narrow linewidth single laser source system for onboard atom interferometry

A compact and robust laser system for atom interferometry based on a frequency-doubled telecom laser is presented. Thanks to an original stabilization architecture on a saturated absorption setup, we obtain a frequency-agile laser system allowing fast tuning of the laser frequency over 1 GHz in few ms using a single laser source. The different laser frequencies used for atom interferometry are generated by changing dynamically the frequency of the laser and by creating sidebands using a phase modulator. A laser system for Rubidium 87 atom interferometry using only one laser source based on a frequency doubled telecom fiber bench is then built. We take advantage of the maturity of fiber telecom technology to reduce the number of free-space optical components (which are intrinsically less stable) and to make the setup compact and much less sensitive to vibrations and thermal fluctuations. This source provides spectral linewidth below 2.5 kHz, which is required for precision atom interferometry, and particularly for a high performance atomic inertial sensor

Quasi full-disk maps of solar horizontal velocities using SDO/HMI data

For the first time, the motion of granules (solar plasma on the surface on scales larger than 2.5 Mm) has been followed over the entire visible surface of the Sun, using SDO/HMI white-light data. Horizontal velocity fields are derived from image correlation tracking using a new version of the coherent structure tracking algorithm.The spatial and temporal resolutions of the horizontal velocity map are 2.5 Mm and 30 min respectively . From this reconstruction, using the multi-resolution analysis, one can obtain to the velocity field at different scales with its derivatives such as the horizontal divergence or the vertical component of the vorticity. The intrinsic error on the velocity is ~0.25 km/s for a time sequence of 30 minutes and a mesh size of 2.5 Mm.This is acceptable compared to the granule velocities, which range between 0.3 km/s and 1.8 km/s. A high correlation between velocities computed from Hinode and SDO/HMI has been found (85%). From the data we derive the power spectrum of the supergranulation horizontal velocity field, the solar differential rotation, and the meridional velocity.Comment: 8 pages, 11 figures, accepted in Astronomy and Astrophysic

A massively parallel OpenFOAM solver for Richards Equation: towards mechanistic modelling of transfers at the watershed scale

We focus on the development and test of a massively parallel OpenFOAM solver for Richards Equation, towards mechanistic modelling of flow and transport phenomena at the watershed scale

Bringing the Firm Back in the Analysis: State-Business Relations in Latin America and their Impact on Policies

The political science literature is now unable to account for the differences in the business community behaviour towards Latin American governments. This thesis offers to fill this gap by answering three questions: what explains the differences between firms’ varying degrees of success and failure in communicating their policy preferences to politicians? What determines the type of policies the business community promotes through lobbying and other political influence mechanisms? What determines business' varying degrees of success and failure in influencing policy outcomes? Answering these questions is essential to understand how political systems respond to powerful private actors and is a condition to the success of political efforts to create a quality jobs led growth. This thesis’ theory answers these questions by developing a typology of the business community’s ability to communicate its preferences to politicians: cartelism, competitive-corporatism, and pluralism. This typology explains the type of interest companies promote and how efficient they are in influencing policies. Conglomerates and large firms (CLFs) lead effective collective action if the benefit of collective action seems high enough, regardless to its cost. Small and medium-sized enterprises (SMEs) organise in business associations if the cost of collective action is low enough, regardless to its benefit. The combination of these two factors shapes the business community’s mode of organisation. If CLFs and SMEs communicate their preferences clearly to politicians, they compete for influence over policies and coordinate ahead of lobbying. In this coordination process, all firms make concessions on their preferred policies to draft more collectively beneficial policy proposals (competitive-corporatism). If only CLFs organise well, they can efficiently promote their own narrow interests, unchallenged (cartelism). When the business community is widely disorganised, the best politically-connected interests prevail (pluralism). Confronted to extensive empirics, this typology better explains trade policy, regulations and fiscal policy in Argentina, Brazil and Colombia

An open source massively parallel solver for Richards equation: Mechanistic modelling of water fluxes at the watershed scale

In this paper we present a massively parallel open source solver for Richards equation, named the RichardsFOAM solver. This solver has been developed in the framework of the open source generalist computational fluid dynamics tool box OpenFOAM® and is capable to deal with large scale problems in both space and time. The source code for RichardsFOAM may be downloaded from the CPC program library website. It exhibits good parallel performances (up to ∼90% parallel efficiency with 1024 processors both in strong and weak scaling), and the conditions required for obtaining such performances are analysed and discussed. These performances enable the mechanistic modelling of water fluxes at the scale of experimental watersheds (up to few square kilometres of surface area), and on time scales of decades to a century. Such a solver can be useful in various applications, such as environmental engineering for long term transport of pollutants in soils, water engineering for assessing the impact of land settlement on water resources, or in the study of weathering processes on the watersheds

LCST-phase behavior and complexation with water of an ionic liquid incorporating the 5-phenyltetrazolate anion

The use of 5-phenyltetrazole, a bioisostere of benzoic acid, as an anion source to prepare an ionic liquid is described for the first time. Tetrabutylphosphonium 5-phenyltetrazolate undergoes phase separation from water with lower critical solution temperature phase behavior, in contrast to completely water miscibletetrabutylphosphonium benzoate, and also exhibits strong complexation with water with both eutectic and peritectic behavior that has not previously been observed in ionic liquid + water systems. The anhydrous and trihydrate salts were isolated and characterized by single crystal X-ray diffraction